1. Field of the Invention
The present invention relates to an inter-vehicle distance control device that performs a vehicle following control by maintaining an inter-vehicle distance from a preceding vehicle.
2. Description of Related Art
In these days, regarding a vehicle such as a car, a technology to recognize an environment around the vehicle using a laser radar or the like and execute a security ensuring, a driving control, and the like has been developed. In particular, as a major practical application of the driving control, there is an automatic inter-vehicle distance control (adaptive cruise control: ACC) system for automatically controlling the vehicle speed or an inter-vehicle distance from a preceding vehicle based on the road condition recognized by the laser radar or the like.
In such an ACC system, when the preceding vehicle slows down and stops while the vehicle is following the preceding vehicle, the vehicle also slows down and stops. In this case, the vehicle following control is released and the operation is switched to a stop maintaining control to maintain the brake to keep the vehicle stopped. When the preceding vehicle starts to move during the stop maintaining control, a driver resets the vehicle following control by manually operating a switch or the like to automatically start the vehicle. This resetting releases the stop maintaining control and starts the vehicle in response to the start of the preceding vehicle.
Regarding the restart of a vehicle following control from a stop maintaining control by resetting the vehicle following control, for example, Japanese Patent Application Laid-Open (JP-A) No. 2008-1337 discloses a technology to disenable the stop maintaining control for a predetermined period of time after releasing the stop maintaining control in a case where the stop maintaining control is released and switched to a vehicle following driving control by operating a lever or the like to start the vehicle. The technology of JP-A No. 2008-1337 is to prevent a case where, when the vehicle following control is reset to start the vehicle but the increase in the vehicle speed is slow, it is determined by mistake that the vehicle is being stopped and the vehicle following control is switched to the stop maintaining control even though the vehicle is moving.
When a stop maintaining control is released and a vehicle following control is restarted, as a typical condition to reset the vehicle following control by accepting a manual operation by the driver, there are conditions where a preceding vehicle speed exceeds a predetermined threshold and a condition where an inter-vehicle distance from the preceding vehicle exceeds a predetermined threshold.
However, in the former condition related to the vehicle speed, resetting may be accepted even when the inter-vehicle distance is small. Thus when the preceding vehicle slows down immediately after the brake is released by resetting, the engine torque may not sufficiently be output and the vehicle may be slipped down backward on a slope or the like.
On the other hand, in the later condition related to the inter-vehicle distance, when the preceding vehicle quickly starts while the inter-vehicle distance is small, resetting is not accepted immediately and the timing of resetting is delayed. Accordingly, the driver may feel that the response is slow and driving comfortability may be deteriorated.